Cámaraite — ideally Ba3NaTi4Fe82+(Si2O7)4O4(OH)4F3 — is triclinic, space group C, a = 10.6965(7) Å, b = 13.7861(9) Å, c = 21.478(2) Å, α = 99.345(1)°, β = 92.315(2)°, γ = 89.993(2)°, V = 3122.6(4) Å3, Z = 4, Dcalc. = 4.018 g cm–3, from the Verkhnee Espe alkaline deposit, Akjailyautas Mountains, Kazakhstan, has been solved and refined to R1 5.87% on the basis of 6682 unique reflections (Fo >4σF). The crystal structure of cámaraite can be described as a combination of a TS block and an intermediate (I) block. The TS (titanium silicate) block consists of HOH sheets (H-heteropolyhedral, O-octahedral), and is characterized by a minimal cell based on translation vectors t1 and t2, with t1 ~5.5 and t2 ~7 Å and t1 ^ t2 close to 90°. We describe the crystal structure of cámaraite using a double minimal cell, with 2t1 and 2t2 translations. In the O sheet, there are eight [6]-coordinated MO sites occupied mainly by Fe2+ and Mn, with minor Fe3+, Mg, Zr, Ca and Zn with <MO–ϕ> = 2.185 Å. Eight MO sites give, ideally Fe82+ p.f.u. In the H sheet, there are four [6]-coordinated MH sites occupied almost solely by Ti (Ti = 4 a.p.f.u.), with <MH–ϕ= = 1.963 Å, and eight [4]-coordinated Si sites occupied solely by Si, with <Si—0> = 1.621 Å. The topology of the TS block is as in Group II of the Ti-disilicates (Ti = 2 a.p.f.u. per minimal cell) in the structure hierarchy of Sokolova (2006). There are six peripheral (P) sites, four [8–12]-coordinated Ba-dominant AP sites, giving ideally 3 Ba p.f.u., and two [10]-coordinated Na-dominant BP sites, giving ideally 1 Na p.f.u. There are two I blocks: the I1 block is a layer of Ba atoms (two AP sites); the I2 block is a layer of Ba (two AP sites) and Na atoms (two BP sites). Along c, there are two types of linkage of TS blocks: (1) TS blocks link via AP cations which constitute the I1 block, and (2) TS blocks link via common vertices of MH octahedra (as in astrophyllite-group minerals) and AP and BP cations which constitute the I2 block. Cámaraite is the only mineral of Group II with two types of linkage of TS blocks and two types of I blocks in its structure. The relation of cámaraite to the Group-II minerals is discussed.

The crystal structure of hejtmanite, Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, from Mbolve Hill, Mkushi River area, Central Province, Zambia (holotype material) has been refined on a twinned crystal to R 1 = 1.88% on the basis of 4539 [|F| > 4|F|] reflections. Hejtmanite is triclinic, C1̅, a = 10.716(2), b = 13.795(3), c = 11.778 (2) ,= 90.07(3),= 112.24(3),= 90.03(3), V = 1612(2) 3. Chemical analysis (electron microprobe) gives: Ta2O5 0.09, Nb2O5 1.27, ZrO2 0.65, TiO2 14.35, SiO2 23.13, BaO 26.68, SrO 0.19, FeO 11.28, MnO 15.12, Cs2O 0.05, K2O 0.33, F 3.82, H2Ocalc. 1.63, O = F 1.61, total 97.10 wt.%, where the H2O content was calculated from the crystal-structure refinement, with (OHF) = 4 apfu. The empirical formula, calculated on the basis of 20 (OF) anions, is of the form (Si2O7)2(XO)4(XP)2, Z=4: (Ba1.82K0.07 Sr0.02)Σ1.91(Mn2.33 Zr0.04Mg0.03)Σ3.95(Ti1.88Nb0.10Zr0.02)Σ2(Si2.02O7)2O2[(OH)1.89 F0.11]Σ2F2. The crystal structure is a combination of a TS (Titanium Silicate) block and an I (intermediate) block. The TS block consists of HOH sheets (Hheteropolyhedral, Ooctahedral). The topology of the TS block is as in Group-II TS-block minerals: Ti ( Nb) = 2 apfu per (Si2O7)2 [as defined by Sokolova (2006)]. In the O sheet, five [6]MO sites are occupied mainly by Mn, less Fe2 and minor Zr and Mg, with <MOφ> = 2.198(φ = O,OH), ideally giving Mn4 apfu. In the H sheet, two [6]MH sites are occupied mainly by Ti, with <MHφ> = 1.962(φ = O,F), ideally giving Ti2 apfu; four [4] Si sites are occupied by Si, with < SiO> = 1.625 . The MH octahedra and Si2O7 groups constitute the H sheet. The two [12]Ba-dominant AP(1,2) sites, with <APφ> = 2.984(φ = O, F), ideally give Ba2 apfu. Two (1,2) and two (1,2) sites are occupied by O atoms and OH groups with minor F, respectively, ideally giving (XO)4 = ()2()2=O2(OH)2 pfu. Two (1,2) sites are occupied by F, giving F2 apfu. TS blocks link via a layer of Ba atoms which constitute the I block. Simplified and end-member formulae of hejtmanite are Ba2(Mn,Fe2)4Ti2 (Si2O7)2O2(OH,F)2 F2 and Ba2Mn4Ti2(Si2O7)2O2(OH)2F2, Z = 4. Hejtmanite is a Mn-analogue of bafertisite, Ba2 4 Ti2(Si2O7)2O2(OH)2F2.